On improving the optical quality of colloidal photonic crystals.
Published: 2004
Language: eng
Number of pages: 207
Description: This work advances the understanding of the impact of lattice disorder on the optical properties of colloidal photonic crystals. It also demonstrates and quantifies improvements in the structural and optical quality of the crystals through refinements of the fabrication techniques.Arrays of colloidal particles were grown on substrates covered with holographic relief gratings realized in photoresist films. When the grating pitch was commensurate with the particle size, a uniform lattice orientation was imposed in the crystals. The enhancement in crystal order was visible for thicknesses as large as 40 layers.The impact of lattice disorder on the optical properties of colloidal photonic crystals was investigated numerically. The greatest impact on the optical properties came from size non-uniformity of colloidal particles. A novel algorithm, based on simulated annealing, was used to generate densely packed arrays of spheres with a given size distribution. When the size standard deviation was larger than 3%, a transition from ordered to random-packed arrangements was observed, along with large and sudden changes in optical properties, in the form of increased scattering and reduced contrast associated with the 111 stopband in transmittance spectra. The abruptness of this transition increased with decreasing index contrast. The numerical results agreed well with experimental results.The enhancement of long-range order was further demonstrated and quantified by optical techniques. The diffraction patterns produced when a collimated laser beam illuminated colloidal crystals were shown to be capable of revealing whether the crystals were mono- or poly-crystalline. Quantitative information about internal ordering was also extracted from diffraction spectra: the photon mean free path in the crystal was estimated to be in the range of 3 to 58 lattice constants, depending on the crystal growth conditions.
Notes: Adviser:  Edward H. Sargent.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 5213.